The invention relates to a reversible speed reducing mechanism for use with hand-held power tools and more particularly to a reversing mechanism for use with power production line tools having a separable motor and gear head which also provides a reduction in speed of three to one to five to one and a concomitant proportional increase in output torque.
Increasing dependence upon the production line method of manufacturing has created an equal dependence upon lightweight hand-held power tools for use by assembly personnel in the manufacturing process. The vast majority of these tools are powered by either compressed air or electricity. Various devices such as gear trains, ratchet mechanisms and impulse devices may be attached to relatively simple high r.p.m. motors to provide energy in the particular form required by a given assembly operation.
One of the most common requirements of such power tools is the ability to reverse the direction of drive in order to facilitate the removal of a threaded fastener which may have been improperly inserted or which must be removed in order to disassemble other components.
In electrically powered tools, directional control is a deceptive problem. It is well known that simply reversing the polarity of electricity to certain windings of the motor will effect directional control and that this can be accomplished by conventional switching means. However, it is seldom appreciated that the rotational speeds of such motors may be as high as 15,000 R.P.M. and that the sudden reversal of motor rotation subjects the driven elements of a tool to severe mechanical shock which materially shortens its life. Secondly, the current surge and back EMF associated with the reversing of the motor necessitates an exceedingly heavy duty reversing switch. Unfortunately, a switch exhibiting the necessary durability is generally bulky and oftentimes fatiguing to the tool operator due to its high activation force.
In the case of the air powered motors, the means most commonly relied upon to provide bidirectional rotation is a vane motor having two inlet ports symmetrically disposed in opposite halves of the vane motor chamber and a common exhaust port positioned midway between the ports. Air entering one inlet port and exiting through the common exhaust port causes the air motor to rotate in one direction whereas air entering the other inlet port and exiting the common exhaust port causes rotation of the motor in the opposite direction. This type of reversing air motor has one drawback. Since the air must enter and exit the vane motor in somwhat less than 180 degrees, the expansive force and thus the power produced by the air motor is less than that which can be produced in a conventional unidirectional motor wherein the radial separation of the inlet and outlet ports allows the effective utilization of the expansive power of the air over approximately 240 degrees. Thus, if the output of an air motor must be bidirectional, a certain amount of output power must be compromised to accomplish it.
The alternative to utilizing a bidirectional air or electric motor in a hand-held tool is incorporating a separate reversing mechanism into a tool having a unidirectional motor. Generally, these devices exhibit lower power output than a unidirectional tool. In this case, the power loss is due to the additional gearing in the reversing mechanism. Such reversing mechanisms also generally add substantially to the weight of the hand-held power tool. In production line work, where an operator may lift and move the tool continuously for several hours, any additional weight markedly increases operator fatigue. Furthermore, the size of the tool is also an important consideration since it is often necessary to operate the tool within the structure being assembled, such as an automobile. A bulky tool which includes the reversing capability required in an application, may, however, be unusuable because it cannot engage or cannot easily be manipulated to engage the fastener or other device it is intended to assemble due to the confined space within which it must function.
If a production process requires slow rotation, the necessary mechanism may be even more complex. Gearing in addition to that necessary to produce bedirectional output rotation may be required and the size and weight of the reversing mechanism may then increase to a point where the tool is intractable for production line use.